diff --git a/src/main/kotlin/io/github/sor2171/puzzles/utils/CatalogStructure.kt b/src/main/kotlin/io/github/sor2171/puzzles/utils/CatalogStructure.kt
index 186c7d4..15d8413 100644
--- a/src/main/kotlin/io/github/sor2171/puzzles/utils/CatalogStructure.kt
+++ b/src/main/kotlin/io/github/sor2171/puzzles/utils/CatalogStructure.kt
@@ -18,9 +18,11 @@ object CatalogStructure {
         arrayOf(
             "${Classification.ALPHABET}.We need a variable, oh, maybe many",
             "${Classification.EXTRA}.More strange variables",
+            "${Classification.EXTRA}.More unpredictable variables",
         ),
         arrayOf(
             "${Classification.ALPHABET}.You need a function, not a mathematical one",
+            "${Classification.EXTRA}.More expressive functions",
         )
     )
 
diff --git a/src/test/kotlin/io/github/sor2171/puzzles/extra/More expressive functions.kt b/src/test/kotlin/io/github/sor2171/puzzles/extra/More expressive functions.kt
new file mode 100644
index 0000000..919e8bf
--- /dev/null
+++ b/src/test/kotlin/io/github/sor2171/puzzles/extra/More expressive functions.kt	
@@ -0,0 +1,32 @@
+@file:SkipCompile(skip = true)
+@file:Suppress("ClassName")
+
+package io.github.sor2171.puzzles.extra
+
+import io.github.sor2171.puzzles.annotation.SkipCompile
+import org.junit.jupiter.api.Test
+
+/**
+ * 本关考察你对 `infix` 和 `operator` 函数的理解。
+ */
+class `More expressive functions` {
+
+    // write start 1
+
+    // write  end  1
+
+    @Test
+    fun puzzle() {
+        val laugh = "Ha" repeatBy 3
+        assert(laugh == "HaHaHa")
+
+        val message = "42" repeatBy 2
+        assert(message == "4242")
+
+        val exclamation = "!" * 4
+        assert(exclamation == "!!!!")
+
+        val combined = ("Yo" repeatBy 2) + ("~" * 3)
+        assert(combined == "YoYo~~~")
+    }
+}
diff --git a/src/test/kotlin/io/github/sor2171/puzzles/extra/More strange variables.kt b/src/test/kotlin/io/github/sor2171/puzzles/extra/More strange variables.kt
index 84db253..9e8e8ce 100644
--- a/src/test/kotlin/io/github/sor2171/puzzles/extra/More strange variables.kt	
+++ b/src/test/kotlin/io/github/sor2171/puzzles/extra/More strange variables.kt	
@@ -8,6 +8,8 @@ import org.junit.jupiter.api.Test
 
 /**
  * 本关考察你对无符号数字的理解。
+ * 
+ * 共两个编写区域。
  */
 class `More strange variables` {
     // write start 1
diff --git a/src/test/kotlin/io/github/sor2171/puzzles/extra/More unpredictable variables.kt b/src/test/kotlin/io/github/sor2171/puzzles/extra/More unpredictable variables.kt
new file mode 100644
index 0000000..dc2e30e
--- /dev/null
+++ b/src/test/kotlin/io/github/sor2171/puzzles/extra/More unpredictable variables.kt	
@@ -0,0 +1,46 @@
+@file:SkipCompile(skip = true)
+@file:Suppress("ClassName")
+
+package io.github.sor2171.puzzles.extra
+
+import io.github.sor2171.puzzles.annotation.SkipCompile
+import org.junit.jupiter.api.Test
+
+/**
+ * 很多初学者认为 `val` 就是“不可变”，但其实它只是“只读（Read-Only）”。
+ * 此外，Kotlin 还提供了属性委托，比如只有在首次访问时才初始化的 `by lazy`。
+ * 本关考察你对 Kotlin 属性（Property）、自定义 Getter 与惰性委托机制的理解。
+ * 
+ * 共两个编写区域。
+ */
+class `More unpredictable variables` {
+    private var accessCount = 0
+    var evalTimes = 0
+
+    val dynamicValue: Int
+        get() {
+            // write start 1
+
+            // write  end  1
+        }
+
+    val lazyGreet: String by lazy {
+        // write start 2
+
+        // write  end  2
+    }
+
+    @Test
+    fun puzzle() {
+        val first = dynamicValue
+        val second = dynamicValue
+        assert(first == 1 && second == 2)
+        assert(dynamicValue == 3)
+
+        assert(evalTimes == 0)
+        assert(lazyGreet == "Hello, Alien!")
+        assert(evalTimes == 1)
+        assert(lazyGreet == "Hello, Alien!")
+        assert(evalTimes == 1)
+    }
+}